In a conventional endoscopic snare operation, an endoscope is inserted into an internal cavity of a patient, e.g., into the colon, and is used to locate abnormal tissue growths such as polyps in the internal cavity. Upon the locating of a polyp or other growth which is to be removed, a wire extending through a tube in the biopsy channel of the endoscope is slid in the distal direction so that a cauterization loop connected to the wire is ejected from the distal end of the tube and the endoscope. The loop and the endoscope are manipulated from outside of the patient to pass the loop over the polyp or growth. The wire is then withdrawn in the proximal direction to tighten the loop around a base region or neck of the polyp. Once the loop is in contact with the base region of the polyp, an electrical current is conducted through the loop via the wire. Generally, as the loop is closed about the base region of the polyp, electrical current is transmitted through the narrowed organic tissues and thereby generates therein heat sufficiently great to cut and cauterize.
Once a polyp is severed by such a snare cauterization technique, it frequently becomes difficult to capture the polyp and retrieve it from the patient. Sometimes the cauterization loop is used in an effort to ensnare the polyp. Other capture techniques involve the use of forceps or the application of suction. In using forceps, the snare cauterization tube is removed from the biopsy channel of the endoscope and replaced with the forceps. The use of a forceps generally prevents one from removing more than a biopsy sample from the patient. The forceps naturally tears off a tissue sample from a severed polyp, leaving the main body of the polyp in the patient. In using suction, a vacuum is applied via a suction channel of the endoscope. The use of suction has the drawback of frequently preventing visual inspection of the patient's internal tissues during withdrawal of the endoscope. The polyp or other tissue mass is drawn against the front end of the endoscope, thus obscuring the light source and the observation lens.
No matter which specific technique is used, the polyp frequently escapes from the capturing instrumentality and falls away into the colon (or other cavity). Especially in cases where the polyp is large, the effort and time expended in retrieving the severed polyp may rival or even exceed the effort and time required to locate and sever the polyp. In some cases, the endoscope must be removed without the polyp and the patient given an enema in an attempt to flush out the polyp from the colon.
Furthermore, there are numerous cases where a severed polyp is never recovered. Sometimes, the polyp is masticated during the retrieval attempt. In all such cases, the pathologist is unable to determine whether the polyp contains carcinoma in situ (localized to the mucosa) or infiltrative carcinoma (spread beyond the muscularis mucosa layer). The patient must then undergo a colon resection, sometimes unnecessarily.
In any event, the manipulations necessary to remove a severed polyp generally increase the trauma to the patient, the expense of the surgery and the hospitalization time. A number of U.S. patents have disclosed techniques for improving snare cauterization operations to facilitate the capture and retrieval of severed polyps. For instance, pursuant to U.S. Pat. No. 5,201,740 of Nakao et al., snare cauterization operations are performed with a surgical instrument assembly comprising a tubular sheath member carrying a metallic cauterization loop and a metal wire operatively connected to the loop, the wire passing longitudinally through the sheath. An electrical supply is operatively connectable to the wire, while a flexible web member is connected to the loop to form a capture pocket, the loop defining a mouth opening of the pocket. During use of the snare cauterization loop, the web member is passed over and substantially surrounds a polyp. The pocket captures the polyp at the same time that the cauterization loop is energized to effectuate a severing of the polyp.
Other improvements are disclosed in U.S. Pat. Nos. 5,190,542, 5,374,273, 5,234,439, 5,782,840, 5,741,271, 5,336,227, 5,486,182, 5,759,187, and U.S. Patent Publication No. 20050085808 all patents to N. Nakao et al.